Sea cucumber

Lore & Background

Sea cucumbers have a leathery skin and an elongated body containing a single, branched gonad; they are named for their overall resemblance to the fruit of the cucumber plant. Like all echinoderms, they have a calcified dermal endoskeleton, usually reduced to isolated microscopic ossicles joined by connective tissue. In some species these can be enlarged to flattened plates forming an armoured cuticle, while in some abyssal or pelagic species the skeleton is absent. Most have five rows of tube feet, though Apodida lacks these and moves by crawling. The mouth is surrounded by tentacles that can be pulled back inside the animal. A remarkable feature is the 'catch' collagen that forms their body wall, which can be loosened and tightened at will, allowing the animal to liquefy its body to squeeze through small gaps and then firm up again.

Reader's Guide

Sea cucumbers are significant as key detritivores in marine ecosystems, recycling nutrients by breaking down organic matter. Their unique collagen-based body wall allows them to inhabit crevices and cracks, contributing to benthic habitat complexity. They are also economically important as a harvested seafood delicacy, particularly in Asian cuisines, where they are known as trepang, namako, bêche-de-mer, or balate. Some species are cultivated in aquaculture systems. Their anatomy, including a water vascular system and respiratory trees that draw water in through the anus, illustrates adaptation to a benthic lifestyle. The absence of a true brain and the presence of a nerve ring that can be surgically removed without impairing movement highlight their decentralized nervous coordination.

Did You Know?

• Sea cucumbers have a 'catch' collagen that can liquefy their body wall to squeeze through small gaps.
• They breathe by drawing water in through the anus and extracting oxygen via respiratory trees.
• Some species, like Pelagothuria natatrix, lack a skeleton and calcareous ring entirely.